Method of producing magnetic recording medium

Abstract

Disclosed is a method of producing a magnetic recording medium which comprises a magnetic layer, comprising a step of kneading a magnetic coating solution containing a ferromagnetic powder and a binder for the magnetic layer under a load of substantial electric power consumption of 0.05 to 0.5 KW per Kg of the ferromagnetic powder in a kneader chamber having an atmospheric water content of not more than 1 g/m 3 .

What is claimed is: 
     
       1. A method of producing a magnetic recording medium including a support and a magnetic layer thereon, said method comprising kneading a magnetic coating solution containing a solvent, a ferromagnetic powder, and a binder for said magnetic layer under an electric power consumption load of 0.05 to 0.5 kw per kg of said ferromagnetic powder in a kneader chamber having an atmospheric water content not exceeding 1 g/m 3  to form a magnetic mix, applying said mix to said support, and drying said mix. 
     
     
       2. The method of claim 1 wherein nitrogen gas is introduced into said chamber during said kneading. 
     
     
       3. The method of claim 2 wherein said nitrogen gas has a dew point of -72° C. and a water content of 2 mg/m 3 . 
     
     
       4. The method of claim 1 wherein said power load is 0.1 to 0.5 kw per kg of said ferromagnetic powder. 
     
     
       5. The method of claim 1 wherein said binder is present in a binder amount, per 100 parts by weight of said ferromagnetic powder, of 3 to 20 parts by weight. 
     
     
       6. The method of claim 5 wherein said binder amount is 6 to 18 parts by weight. 
     
     
       7. The method of claim 6 wherein said binder amount is 9 to 16 parts by weight. 
     
     
       8. The method of claim 7 wherein said power load is 0.2 to 0.5 kw per kg of said ferromagnetic powder. 
     
     
       9. The method of claim 1 wherein said solvent is present in a solvent amount, per 100 parts by weight of said ferromagnetic powder, of 10 to 60 parts by weight. 
     
     
       10. The method of claim 9 wherein said solvent amount is 20 to 55 parts by weight. 
     
     
       11. The method of claim 10 wherein said solvent amount is 30 to 50 parts by weight. 
     
     
       12. The method of claim 1 wherein said ferromagnetic powder has Fe, Ni, Co, or mixtures thereof as a principal component. 
     
     
       13. The method of claim 12 wherein said ferromagnetic powder is an Fe--Al alloy, an Fe--Ni alloy, or a mixture thereof. 
     
     
       14. The method of claim 1 wherein said ferromagnetic powder has a BET specific surface area of at least 45 m 2  /g. 
     
     
       15. The method of claim 1 wherein said binder is a resin selected from the group consisting of polyethylene, polyesters, and vinyl chlorides. 
     
     
       16. The method of claim 15 wherein said binder contains a repeating unit having at least one polar group selected from the group consisting of --SO 3  M', --OSO 3  M', --COOM' and --PO(OM") 2 , wherein M" represents hydrogen or an alkali metal, M' represents hydrogen, an alkali metal, or an alkyl group.